Question

What is a lactometer?

Answer 1

A lactometer is an instrument which works according to the Archimedes’ principle. Whenever an object is immersed in a fluid, a buoyant force acts on it and this buoyant force is described by the Archimedes’ principle and the force is related to the density and volume of the fluid and acceleration due to gravity.

Complete answer:
Lactometer is an instrument which is used to test the purity of milk .It works on the principle of Archimedes’ principle.
According to the Archimedes’ principle, when a solid object is immersed in a liquid, the buoyant force acting on it is equal to the fluid displaced by it. Therefore, objects having lower density than the fluid float on it while the objects having greater density sink in it. According to the Archimedes’ principle, the buoyant force is given by-
${{F}_{b}}=-\rho gV$
Here, ${{F}_{b}}$ is the buoyant force
$\rho$ is the density of fluid
$V$ is the volume of the fluid
The lactometer measures the density of milk relative to the density of water. If the density of milk falls within the approved range then the milk is pure otherwise it contains adulteration.
Therefore, the lactometer is a device used to check the purity of milk using Archimedes’ principle.

Note:
The resultant force acting on a body immersed in a fluid is the resultant between buoyant force and the force of gravity that is why we say that there is a loss in weight. When the force of gravity is more than the buoyant force, the object sinks otherwise the object floats.